You could use a logic gate setup between the rx pins of the lcd's and the 8052, to block or allow the comm port to communicate with it, such as a 74HCT4066 an analogue switch. This would only need one extra pin to switch between the two lcd's.

If the lcd returns data then just put another set of 74hct4066's between each tx pin on the lcd and the rx pin of the 8052. Plus as the 4066 has four switchs per chip you would only require one.

Steve